Apparatus for flaking and surfacing wood



March 15, 1966 D. 1.. JOHNSON 3,240,245

APPARATUS FOR FLAKING AND SURFACING WOOD Filed May 10, 1963 4 Sheets-Sheet l INVEN DONALD L JOH ON ATTORNEY March 15, 1966 r n. 1.. JOHNSON APPARATUS FOR FLAKING AND SURFACING WOOD 4 Sheets-Sheet 2 Filed May 10, 1963 FIG.

IN VEN TOR. DONALD L. JOHNSON ATTOR NEY March 15, 1966 I JQHNSQN 3,240,245

APPARATUS FOR FLAKING AND SURFACING WOOD Filed May 10, 1963 4 Sheets-Sheet 5 FIG. 8

FIG. IO

[Q INVENTOR. DONALD L. JOHNSON ATTORNEY March 15, 1966 JOHNSON 3,240,245

APPARATUS FOR FLAKING AND SURFACING WOOD Filed May 10, 1963 4 Sheets-Sheet 4 Q Q !.A.A"?A*."

27 INVENTO DONALD L. JOHN N TTORNEY United States Patent 3,240,245 APPARATUS FOR FLAKING AND SURFACING WOOD Donald L. Johnson, 1340 Heatherwood W., Tacoma, Wash. Filed May 10, 1963, Ser. No. 27 9,411 9 Claims. (Cl. 144176) This invention, like the inventions described in my prior US. Letters Patents No. 2,889,859, issued June 9, 1959, No. 2,949,946, issued August 23, 1960, and No. 2,964,- 079, issued December 13, 1960, relates to the producing of special wood flakes while cutting a flat surface on wood through the employment of a rotating cutter head having Wood-slicing knives with their cutting edges arranged in a helical-spiral, radially-retreating and axially-advancing cutting path, with the wood, from which the flakes are cut, being moved during the cutting relatively with respect to the cutter head in a direction perpendicular to the axis of rotation of the cutter head and at a speed properly synchronized with the speed of rotation of the particular cutter head,

While the devices described in the prior patents above mentioned are capable of cutting the desired flat surface on wood and of producing wood flakes in the cutting, they have been found to be somewhat costly and difficult to manufacture, they have presented certain maintenance problems, and the quality of the wood flakes which they produce is somewhat below that which it has been possible to obtain by such method and inferior to the flakes now obtainable with the improved apparatus of the present invention.

One objection to the cutter head assemblies described in these prior patents is the fact that the straight outer edges of the knife bars in the cutter heads (for example, the straight outside edges of the knife bars 12 of the apparatus described in US. Letters Patent No. 2,949,- 946,) do not actually conform to the outer edge of the curved radially-retreating, axially-advancing path in which the knives move. It has been found that the contact of such straight outer edges of the knife bars with the wood in the severing of the corresponding ends of the wood flakes has a tendency to cause rough, frayed or torn ends in the flakes, and furthermore it has been found that such straight outer edges of the knife bars have limited the depth of the cut in the wood which can be made by each rotation of the cutter head.

Accordingly an object of the present invention is to provide an improved cutter head assembly in a device of this type in which the outer edges of the knife bars will be curved instead of straight, and with the curvature of such outer edges conforming substantially to the spiral cutting line of the cutter head assembly.

Another object of the invention is to provide an improved cutter head assembly having improved and novel cutting knives, the cutting edges of which can be sharpened more easily and efliciently, and with which knives the uniform shape and weight of the knives can be more effectively maintained for proper balancing of the cutter head.

A related object is to provide an improved cutter head assembly which can more easily be maintained and serviced and which at all times will be highly reliable in use from the standpoint of safety.

A further object of the invention is to provide a cutter head assembly of the type indicated which will be more compact in construction and capable of being produced more easily.

In some cases, with certain species of wood, and with different desired thicknesses of wood flakes, it is desirable to have the slicing knives provided with different types of spurs for scoring, cutting or severing the ends of 3,249,245 Patent ed Mar. 15, 1966 the wood flakes. An additional object of this invention is provide improved cutting knives which can be made to include desired cutting or scoring spurs on their outer edges, which spurs will have their outer peripheries also curved to conform to the curvature of the outer edges of the knives and the spiral cutting line of the cutter head, and which spurs will be capable of being ground to special shapes with the grinding of the knives in order that the spurs may be specifically suitable for the manner in which it is desired to have the ends of the particular wood flakes which are being made severed from the mass of wood in the cutting of the flakes.

The manner in which and the means by which these objects are attained with the improved knives and apparatus of the present invention, the particular shape and special mounting of the knife bars in the cutter head, and th special spurs which it is practical to provide as an integral part of the knives, will be explained in and described with reference to the accompanying drawings forming part of this specification.

In the drawings:

FIG. 1 is a diagrammatic view illustrating in general the operation :of the cutter head in producing the desired wood flakes while also cutting the desired fiat surface on a log of wood;

FIG. 2 is an elevational view of the working face f the cutter head assembly of the present invention, with a portion thereof broken away for clarity, the cutter head being shown as provided with three cooperating series of knife bars having their pairs of cutting edges in helicalspiral knife lines, and showing in part the manner in which the knife bars are clamped in desired position in special slots provided in the cutter head body;

FIG. 3 is a developed side view of the cutter head assembly, drawn to a larger scale, showing that portion of the cutter head indicated by the line 33 in FIG. 2;

'FIG. 4 is an elevation showing the lower face of one of the special knife bars for the cutter head, showing the pair of beveled cutting knife blades, the curved outside edge and correspondingly curved inside edge of the knife bar, and the curved peripheral spur on the outside edge of each of the beveled cutting knife blades;

FIG. 5 is an elevation showing the opposite or upper face of the knife bar of FIG. 4;

FIG. 6 is a partial sectional View on line- 66 of FIG. 4;

FIG. 7 is a fragmentary section on line 7-7 of FIG. 4 drawn to a larger scale;

FIG. 8 is a fragmentary side elevation taken on line 88 of FIG. 2 drawn to a larger scale;

FIG. 9 is a fragmentary section taken along one of the knife-receiving slots in the body of the cutter head, taken on the line indicated at 99 in FIG. 3, and showing the knife bar of FIG. 4 in place in the cutter head slot;

FIG. 10 is a fragmentary transverse section across one of the knife slots in the cutter head body, and taken on the line indicated at Ill-10 in FIG. 3;

FIG. 11 is a more or less diagrammatic elevation, drawn to a much smaller scale, showing the body of the cutter head mounted in a simple fixture in a lathe assembly to illustrate the manner in which the knife-holding slots and inwardly-extending slits are formed in the body of the cutter head;

FIG. 12 is an elevation showing the upper face of a knife bar formed with a pair of continuous peripheral spurs on the upper face, in contrast to the single spur shown on the lower face of the knife bar of FIG. 4;

FIG. 13 is a fragmentary section on line 13-13 of FIG. 12 drawn to a considerably enlarged scale;

FIG. 14 is a diagrammatic elevation, drawn to an enlarged scale, illustrating the action of the beveled knife blade of a knife bar in shearing a wood flake when the knife blade is not provided with any peripheral spur;

FIG. 15 is a similar elevation illustrating the action of a knife blade when the knife blade is formed with a peripheral scoring spuring such as shown on the knife blade of FIG. 4;

FIG. 16 shoWS a knife blade with a tearing type of peripheral spur;

FIGURE 17 shows a knife with a peripheral spur for performing a combined tearing and scoring action for the ends of the flakes being cut; and

FIG. 18 illustrates the action of a knife blade having a continuous cutting spur projecting away from the surface being cut, such as the spurs shown on the knife bar of FIGS. 12 and 13.

Referring first to FIGS. 1 and 2, the cutter head body 10, as shown in the drawings, is formed with a plurality (thus 3 in this case) of identical volute portions each extending for 120 on the periphery of the cutter head, with the radius in each portion decreasing in the direction opposite the direction of rotation of the cutter head, the cutter head being similar in this respect to the cutter heads described in the prior patents previously mentioned. Each volute portion is provided with 6 knife bars, each knife bar having a pair of knife blade cutting edges, indicated at 1 to 6. inclusive.

A series of identical, equally-spaced knife slots 11 and continuing inner slits (see also FIGS. 3, 8, 9 and 10) are cut in each volute peripheral portion of the cutter head body and extend in oblique planes from one face of the cutter head to the other. The cross sectional shape of these slots is shown best in FIG. 10. It will be noted that the slots decrease in width inwardly and that the upper side wall of each slot, thus the side wall of the slot more remote from the working face of the cutter head, is formedwith serrations 13 extending the entire length of the slot. A narrow slit 12 extends inwardly from the bottom of each slot extending in a plane parallel to the plane of the lower side of the slot. These slots and slits, as previously indicated, extend in planes which are inclined at a suitable acute angle (for example, an angle of 25) with the faces of the cutter head or with a plane perpendicular to the axis of rotation of the cutter head, and this angle of inclination constitutes the desired cutting angle for the knives.

A very important and novel feature of the present invention, however, is the fact that slots 11 and their related inner slits 12 are curved in their respective planes. In other words, the bottom of each slot, and similarly the bottom of each slit, extends along a curved path instead of extending in a straight line.

The manner in which these parallel slots and slits are cut in the peripheral portions of the cutter head body is indicated diagrammatically in FIG. 11, wherein the cutter head body 10 is shown carried on a supporting assembly 14 at a desired angle (for example 25) with the horizontal plane of a cutter (indicated at 15) which rotates on a verticalaxis. The supporting assembly with the cutter head body 10 mounted thereon is rotated also on a vertical axis as to bring the inclined cutter head into and out of the path of the rotating cutter 15 and thus cause a curved slot to be cut in the cutter head. Then the position of the cutter head in the supporting assembly is adjusted and the operation is repeated for the next successive slot, and so on.

The purpose of having the knife bar slots 11 curved in their respective planes in the cutter head body, instead of having them extend in straight paths in these planes like the knife bar slots in the previously mentioned prior patents, is to enable knife bars with curved peripheries to be employed in place of knife bars having straight outer edges such as those described in the prior patents.

FIGS. 4 and show such an improved double knife bar 16 adapted for use in accordance with the present invention. This knife bar, like the knife bar shown in FIGS. 15 and 16 of US. Letters Patent No. 2,949,946 is provided with a pair of separate cutting knife blades 18 and 19, but, unlike the knife bar in this earlier patent, the outer and inner edges 17 and 17, instead of being straight, constitute arcs of concentric circles. It will be noted from FIGS. 5, 6 and 10 that the shape and size of the slots 11 in the cutter head body correspond to the cross sectional shape and size of the inner or root portion of the knife bar 16. Serrations 21 are provided extending along the upper side of the root portion of the knife bar to mate with the serrations 13 along the upper wall of the slots 11. Thus the knife bars are mounted in the cutter head by being tapped into place from the back or top of the cutter head until the cutting edges of the blades are in proper location for the desired axiallyadvancing, radially-retreating cutting paths. As a guide in the proper setting of the knife bars, set-up lines, as indicated at 22 in FIG. 3, are machined in the peripheral portions of the cuter head body to mark the proper location for the cutting edges of the blades.

The slits 12 (FIGS. 2, 3, 9 and 10) which extend inwardly into the cutter head body from the bottoms of the slots 11, are traversed by clamping bolts 23 which extend parallel to the axis of rotation of the cutter head, the slits thus extending beyond the clamping bolt holes. Since the root portions of the knife bars have the same cross sectional shape and dimensions as the knife bar slots 11, a slight tightening of the clamping bolts 23 is all that is required for securing the knife bars rigidly in place in the cutter head body. The curvature of the outer periphery 17 of the knife bars preferably corresponds approximately to that of an are having as its radius the mean radius of the volute portions of the cutter head periphery. Such curvature is sufficiently accurate for carrying out the objects of this invention.

The fact that the outer and inner peripheries of the knife bars are curved instead of straight and that the knife slots are correspondingly curved, results in several advantages. The outer edges of the knife bars conform quite closely to the outer edge of the path through which the knife blades move, and the desirability of this from the standpoint of efficiency in the cutting of the wood flakes has already been indicated. The sharpening of the knife blades does not cause any variation in the path of the peripheries of the knife blades. The proper and eflicient sharpening of the knife blades, the maintenance of uniform shape and weight of the knife bars, and the maintenance of proper balance in the entire cutter head assembly present less of a problem. Since the slots are curved instead of being straight, there is no tendency for the knife bars to slide out from their slots with the rapid rotation of the cutter head, even in the event of failure to tighten the clamping bolts 23. The mounting of the knife bars in place is done more quickly and more easily and the entire cutter head assembly is more compact and of simpler construction than the corresponding cutter head assemblies described in the prior patents previously referred to.

With some species of wood, and with certain thicknesses of flakes, the use of knives without any special spur for cutting the outer ends of the flakes will prove entirely satisfactory. The knives in such case perform what may be described as a simple shearing action, as. illustrated by the knife 24 in FIG. 14. On the other hand, in other cases it has been found more satisfactory to provide the knives with special spurs to aid in the severing of the outer ends of the flakes as they are cut or sliced by the knives. Such spurs may be so designed as to perform a scoring, tearing or cutting action, or a combined tearing and scoring action. With the improved knife bars of the present invention it is more feasible to have various types of peripheral spurs which will function in the par ticular manner desired in connection with the severance of the ends of the flakes. Regardless of the type of peripheral spurs selected for use in a particular case, the

fact that the outer or peripheral edge of the spur will be curved with the outer peripheral edge of the knife bar, instead of being straight (like the spurs 26 in US. Letters Patent No' 2,964,079), facilitates the easy and smooth entry of the spur into the wood along the outer edge of the helical-spiral path in which the wood flakes are cut.

FIG. illustrates the operation of the knife blade 16 with the spur 20 shown in FIG. 4. In this case the spur 20 performs what may be described as a scoring action for the outer end of the flake which will be cut by the next successive knife.

In FIG. 16 the spur on the outer periphery of the knife 26 perform-s what may be described as a tearing action for the end of the flake to he cut by the next successive knife. In general, when thicker wood flakes are to be cut for pulping use it is desirable to open the end grain in each flake, and for this purpose a tearing spur is more suitable than a scoring type of spur such as shown in FIG. 15, since the scoring type of spur has a tendency to compress the grain in the end of the flake instead of opening the grain. However, it will be apparent that, if the spur 25 in FIG. 16 had its outer periphery straight instead of curved, the engagement of the straight outer edge with the wood bordering on the path at which the flakes are being cut, would have at least as much tendency to compress the end grain along the adjoining subsequent cutting path as to open such grain in the wood.

FIG. 17 shows a special spur 27 on the knife 28 which is designed to perform a combined tearing and scoring action for the ends of the flakes, inasmuch as this special spur tears out a tiny piece from the end of the flake and also scores the rest of the end portion.

Where it is desired to have the ends of the flakes cut off as the flakes are sliced from the wood by the knives, then elongated knife-like spurs 30 and 31, as shown on the knife bar 2? in FIGS. 12 and 13, may be provided. In this case, however, the spurs are located on the top face of the knife and project away from the surface being cut instead of projecting towards such surface as in the case of the previously described spurs. The manner in which the cutting spur of this type acts is illustrated in FIG. 18. The cutting spur extends forwardly as well as upwardly from the cutting edge of the knife and continues along the curved periphery of each cutting edge portion. Obviously satisfactory results would not be obtained with cutting spurs of this particular type unless the periphery of the knife and the periphery of the cutting spur were curved so as to conform substantially with the edge of a helical-spiral operating path of the cutter head assembly.

It would be possible to have further modifications in the types of peripheral spurs formed on the knife, but those illustrated have been found to be the ones most likely to be used for different species of wood, different thicknesses of flakes, and for types of flakes for different end uses.

I claim:

1. In a device of the character described for flaking and surfacing wood, a rotating cutter head having its periphery formed into a plurality of identical volute portions each having a radius decreasing constantly in the direction opposite from the direction of rotation, said volute portions having equally spaced slots, each of said slots extending in a single plane, said slots inclined forwardly in the direction of rotation of said cutter head, the planes of said slots all having the same angularity with the cutter head axis, knife bars secured in said slots respectively, each knife bar extending in a single plane, each knife bar and the slot in which it is mounted defining a plane elongated in the same direction, said knife bars having straight cutting knife blades extending substantialiy radially outwardly from said cutter head, said knife bars so positioned in their respective slots that said cutting knife blades will be arranged in paths advancing axially toward the work in the direction opposite from the direction of rotation of said cutter head, the outer peripheral non-cutting edges of said knife bars extend ing from the outer ends of said blades being curved and elongated in their respective planes and constituting arcs of identical circles, the curvature of said non-cutting peripheral edges also corresponding substantially to the curvature of the outer periphery of the path cut by said cutting blades in the work as the work is moved relatively with respect to the cutterhead axis in a direction perpendicular to said axis at a speed properly synchronized with the speed of rotation of the cutterhead, and the bottoms of said slots and the inner peripheral edges of said knife bars in said slots constituting arcs of identical circles and arcs of circles concentric with the circles of the arcs of said outer non-cutting peripheral edges respectively of said knife bars.

2. In a device of the character described for flaking and surfacing wood, a rotating cutter head having its periphery formed into a plurality of identical volute portion-s each having a radius decreasing constantly in the direction opposite from the direction of rotation, said volute portions having identical, equally spaced slots extending from the working face to the opposite face of said cutter head, each of said slots extending in a single plane, said slots inclined forwardly in the direction of rotation of said cutter head, the planes of said slots all having the same angularity with the cutter head axis, knife bars carried in said slots respectively, each knife bar extending in a single plane, each knife bar and the slot in which it is mounted defining a plane elongated in the same direction, said knife bars having straight cutting knife blades extending substantially radially outwardly from said cutter head, said knife bars so positioned in their respective slots that said cutting knife blades will be arranged in paths advancing axially towards the work in the direction opposite from the direction of rotation of said cutter head, the outer peripheral non-cutting edges of said knife bars extending from the outer ends of said blades being curved and elongated in their respective planes and constituting arcs of identical circles, the curvature of said non-cutting peripheral edges corresponding substantially to the curvature of the outer periphery of the path cut by said cutting blades in the work as the work is moved relatively with respect to the cutterhead axis in a direction perpendicular to said axis at a speed properly synchronized with the speed of rotation of the cutterhead, the bottoms of said slots and the inner peripheral edges of said knife bars in said slots constituting arcs of identical circles and concentric with the circles of the arcs of said outer non-cutting peripheral edges of said knife bars respectively, said knife bars having mounting portions fitting in said slots of the same cross sectional size as said slots, mating serrations extending along said inner portions of said knife bars and along a wall of each slot, a slit extending into said cutter head from the bottom of each slot, and clamping bolts in said cross head crossing said slits.

3. In a device of the character described for flaking and surfacing wood, a rotating cutter head having its periphery formed into a plurality of identical volute portions each having a radius decreasing constantly in the direction opposite from the direction of rotation, said volute portions having identical, equally spaced slots extending from the working face to the opposite face of said cutter head, each of said slots extending in a single plane, said slots inclined forwardly in the direction of notation of said cutter head and the planes of said slots all having the same angularity with the cutter head axis, knife bars carried in said slots respectively, each knife bar extending in a single plane, each knife bar and the slot in which it is mounted defining a plane elongated in the same direction, said knife bars having straight cutting knife blades extending substantially radially outwardly from said cutter head, said knife bars so positioned in their respective slots that said cutting knife blades will be arranged in paths advancing axially towards the work in the direction opposite from the direction of rotation of said cutter head, the outer peripheral non-cutting edges of said knife bars being curved and elongated in their respective planes and constituting arcs of identical circles, the bottoms of said slots and the inner peripheral edges of said knife bars in said slots constituting arcs of identical circles and concentric with the circles of the arcs of said outer non-cutting peripheral edges of said knife bars respectively, said knife bar's having mounting portions fitting in said slots of the same cross sectional size as said slots, mating serrations extending along said inner portions of said knife bars and along a wall of each slot, a slit extending into said cutter head from the bottom of each slot substantially in the same plane with the slot and the knife bar, the bottoms of said slits being .curved, the bottoms of said slits constituting arcs of circles concentric with the circles of the arcs of said bottoms of said slots and said inner edges of said knife bars, and clamping bolts in said cross head beyod the bottoms of said slots, said clamping bolts crossing said slit-s and extending substantially parallel to the axis of said cross head.

4. The combination set forth in claim 3 with said volute peripheral portions of said cutter head marked with setup lines to guide the positioning of said straight cutting knife blades of said knife bars and thereby the positioning of said knife bars in their respective slots, whereby said cutting blades of said knife bars will be located in the desired axially-advancing lines in said peripheral portions of said cutter head when said knife bars are set in place in their slots.

5. The combination set forth in claim 3 with the addition of spurs at the outer ends of said straight cutting blades of said knife bars, said spurs having curved outer peripheries coinciding with the outer peripheral non-cutting edges of said knife bars extending from the outer ends of said blades.

6. The combination set forth in claim 3 with the addition of spurs at the outer ends of said straight cutting blades of said knife bars, said spurs having curved outer peripheries coinciding with the outer peripheral noncutting edges of said knife bars, and said spurs projecting towards the surface being cut by said knife blades for delivering a scoring action along the outer periphery of the path being cut by said cutting blades and facilitating the severing of the outer ends of the resulting wood flakes produced by said flakes.

7. The combination set forth in claim 3 with the addi tion of spurs at the outer ends of said straight cut-ting blades of said knife bars, said spurs having curved outer peripheries coinciding with the outer peripheral non-cutting edges of said knife bars, said spurs constituting additional small knife blades extending downwardly from outer ends of said first mentioned blades of said knife bars, into the surface to be cut by said first mentioned blades of said knife bars and also projecting forwardly beyond said first mentioned blades of said knife bars in the direction of rotation of said cutter head to produce a tearing action along the outer ends of the wood flakes.

8. The combination set forth in claim 3 with the addition of spurs at the outer ends of the straight cutting blades of said knife bars, said spurs having curved outer peripheries coinciding with the outer peripheral non-cutting edges of said knife bars, said spurs projecting downwardly from the outer ends of said blades of said knife bars, each spur having a knife point located forwardly and below the respective knife blade, said spurs producing a combined tearing and scoring action on the outer ends of the wood flakes preparatory to the cutting of the wood flakes by the knife blades.

9. The combination set forth in claim 3 with the addition of spurs at the outer ends of said straight cutting edges of said blades of said knife bars, said spurs having curved outer peripheries coinciding with the outer peripheral non-cutting edges of said knife bars, each of said spurs extending forwardly and upwardly from the outer end of the respective knife blade for the purpose of cutting the outer ends of the wood flakes as the flakes are sliced from the wood by the knife blades.

References Cited by the Examiner UNITED STATES PATENTS 841,439 1/1907 Plue 144-221 1,194,865 8/1916 Muller 144-230 2,129,417 9/1938 Gase 144-221 2,468,562 4/1949 Lank 144-219 2,889,859 6/1959 Johnson 144176 2,922,448 1/1960 Standal 144-219 2,949,946 8/1960 Johnson 14416-2 2,964,079 12/1960 Johnson 144176 LESTER M. SWINGLE, Primary Examiner.

WILLIAM W. DYER, 111., ROBERT C. RIORDON,

Examiners. 

1. IN A DEVICE OF THE CHARACTER DESCRIBED FOR FLAKING AND SURFACING WOOD, A ROTATING CUTTER HEAD HAVING ITS PERIPHERY FORMED INTO A PLURALITY OF IDENTICAL VOLUTE PORTIONS EACH HAVING A RADIUS DECREASING CONSTANTLY IN THE DIRECTION OPPOSITE FROM THE DIRECTION OF ROTATION, SAID VOLUTE PORTIONS HAVING EQUALLY SPACED SLOTS, EACH OF SAID SLOTS EXTENDING IN A SINGLE PLANE, SAID SLOTS INCLINED FORWARDLY IN THE DIRECTION OF ROTATION OF SAID CUTTER HEAD, THE PLANES OF SAID SLOTS ALL HAVING THE SAME ANGULARITY WITH THE CUTTER HEAD AXIS, KNIFE BARS SECURRED IN SAID SLOTS RESPECTIVELY, EACH KNIFE BAR EXTENDING IN A SINGLE PLANE, EACH KNIFE BAR AND THE SLOT IN WHICH IT IS MOUNTED DEFINING A PLANE ELONGATED IN THE SAME DIRECTION, SAID KNIFE BARS HAVING STRAIGHT CUTTING KNIFE BLADES EXTENDING SUBSTANTIALLY RADIALLY OUTWARDLY FROM SAID CUTTER HEAD, SAID KNIFE BARS SO POSITIONED IN THEIR RESPECTIVE SLOTS THAT SAID CUTTING KNIFE BLADES WILL BE ARRANGED IN PATHS ADVANCING AXIALLY TOWARD THE WORK IN THE DIRECTION OPPOSTE FROM THE DIRECTION OF ROTATION OF SAID CUTTER HEAD, THE OUTER PERIPHERAL NON-CUTTING EDGES OF SAID KNIFE BARS EXTENDING FROM THE OUTER ENDS OF SAID BLADES BEING CURVED AND ELONGATED IN THEIR RESPECTIVE PLANES AND CONSTITUTING ARCS OF IDENTICAL CIRCLES, THE CURVATURE OF SAID NON-CUTTING PERIPHERAL EDGES ALSO CORRESPONDING SUBSTANTIALLY TO THE CURVATURE OF THE OUTER PERIPHERY OF THE PATH CUT BY SAID CUTTING BLADES IN THE WORK AS THE WORK IS MOVED RELATIVELY WITH RESPECT TO THE CUTTERHEAD AXIS IN A DIRECTION PERPENDICULAR TO SAID AXIS AT A SPEED PROPERLY SYNCHRONIZED WITH THE SPEED OF ROTATION OF THE CUTTERHEAD, AND THE BOTTOMS OF SAID SLOTS AND THE INNER PERIPHERAL EDGES OF SAID KNIFE BARS IN SAID SLOTS CONSTITUTING ARCS OF IDENTICAL CIRCLES AND ARCS OF CIRCLES CONCENTRIC WITH THE CIRCLES OF THE ARCS OF SAID OUTER NON-CUTTING PERIPHERAL EDGES RERESPECTIVELY OF SAID KNIFE BARS. 